1. Field of the Invention
The present invention generally relates to cryopumps, sputtering apparatuses, and semiconductor manufacturing apparatuses. More specifically, the present invention is related to a cryopump used to form a vacuum inside of a vacuum chamber, such as a processing chamber, a sputtering apparatus using the cryopump, and a semiconductor manufacturing apparatus having the cryopump.
2. Description of the Related Art
Conventionally and continuously, a multistage type cryopump has been used as a vacuum pump for forming an oil-less and clean vacuum state for manufacturing an LSI (large scale integrated circuit), a VLSI (very large scale integrated circuit), or the like.
Such a cryopump is connected to a vacuum chamber such as a processing chamber where process gas flows. The cryopump absorbs and condenses gas in the vacuum chamber on a cryogenic surface so that the vacuum state is formed. See Japanese Laid-Open Patent Application Publication No. 5-312149.
FIG. 1 is a partial cross-sectional view of a related art cryopump using a cooling storage type cryocooler.
As shown in FIG. 1, a cryopump includes a two-stage type GM (Gifford-McMahon) cycle cryocooler 51 (hereinafter “cryocooler 51”) and a helium compressor 52. The helium compressor 52 is connected to the cryocooler 51 via a gas tube 53. A low temperature part of the cryocooler 51 is inserted in an adiabatic vacuum external cylinder 61. In addition, a vacuum chamber such as a processing chamber not shown in FIG. 1 is connected to the adiabatic vacuum external cylinder 61.
The cryocooler 51 includes a first cooling stage 54 and a second cooling stage 55.
A first condensing panel 56 as a first cooling panel is provided at the first cooling stage 54. Louvers 60 are provided at the first condensing panel 56 at an upper part of the cryopump 58 with a gap. The first condensing panel 56 and the louvers 60 are cooled at, for example, approximately 80 K, so that a gas composition having a relatively high freezing point (solidifying point), such as moisture or carbon dioxide gas in the vacuum chamber, is condensed.
A cryopanel 58 is provided at the second cooling stage 55 and cooled at, for example, approximately 20 K. Because of this, gas having a lower freezing point (solidifying point), such as nitrogen or argon in the vacuum chamber, is condensed at the cryopanel 58. In addition, in order to form an ultra-high vacuum, it is necessary to discharge hydrogen or helium having a further lower freezing point (solidifying point). In this case, activated carbon 59 is adhered to a part of the cryopanel 58. The activated carbon 59 absorbs gas such as hydrogen or helium.
In addition, the cryopanel 58 where the gas composition is accumulated by condensation or absorption is regenerated at a desirable time. This regeneration is implemented by, for example, increasing temperatures of the first condensing panel 56 and the cryopanel 58 to designated temperatures and discharging the gas which is condensed and absorbed from the cryopanel 58. A time for cooling in order to increase the vacuum again after this is called “cooling down time”.
However, in the related art cryopump, the first condensing panel 56 is made of a single material. Normally, the first condensing panel 56 is made of copper (Cu) or aluminum (Al).
In a case where the first condensing panel 56 is made of copper (Cu), the heat capacity is larger than that in a case where the thermal shield is made of aluminum (Al). Therefore, a long cooling down time is required at the time of regeneration and therefore it is not possible to implement regeneration with high efficiency.
Details of this are discussed below. The thermal capacity is a quantity of heat required when the temperature of a material is increased by 1° C., and is the product of mass multiplied by specific heat in a case of a uniform material.
Assuming that the temperature of the thermal shield is 300 K; the volume of the thermal shield is V (cm3); the specific heat of copper (Cu) is 400 (J/KgK); the specific heat of aluminum (Al) is 900 (J/KgK); the density of copper (Cu) is 8.96×10−3 (Kg/cm3); and the density of aluminum (Al) is 2.69×10−3 (Kg/cm3), the thermal capacity of copper (Cu) is V (cm3)×8.96×10−3 (Kg/cm3)×400 (J/KgK)=3.584×V (J/K). In this case, the thermal capacity of aluminum (Al) is V (cm3)×2.69×10−3 (Kg/cm3)×900 (J/KgK)=2.42×V (J/K).
Thus, in the case where the first condensing panel 56 is made of copper, the heat capacity is larger than that in the case where the first condensing panel 56 is made of aluminum (Al).
On the other hand, in the case where the first condensing panel 56 is made of aluminum (Al), the temperature gradient between the first cooling stage 54 of the cryocooler 51 and the louvers 60 is high.
In other words, since the coefficient of thermal conductivity of aluminum (Al) is lower than that of copper (Cu), for example, high temperature process gas comes in contact with the louver 60 so that the temperature of the louver 60 is increased and therefore the cooling effect generated at the first cooling stage 54 of the cryocooler 51 is not extended to the louver 60.
Because of this, the louver 60 cannot be cooled, efficiently and the gas composition in the vacuum chamber which should be absorbed by the louvers 60 reaches the cryopanel 58 without sufficient condensation.
As a result of this, the condensation and absorption of the gas composition by the cryopanel 58 are not implemented efficiently and therefore it may be not possible to make the vacuum chamber have a desirable vacuum degree.